This invention relates to position determination systems. Specifically, the present invention relates to an apparatus and a method for indicating a skyplot.
Satellite positioning system (SATPOS) devices that determine position using the satellites of the US Global Positioning System (GPS) are commonly used for navigation of vessels, vehicles, airplanes, and other conveyances. SATPOS devices are also used for surveying, construction site planning and management, mining, oil and gas exploration and development, etc. Also, handheld SATPOS devices are used for personal navigation, data collection, data maintenance, etc.
SATPOS devices are quite effective for indicating the position of the SATPOS device. Position is typically indicated using either an alphanumeric indication of position or by displaying a map that indicates position. Alphanumeric indications of position typically include coordinates such as, for example, Latitude and Longitude, World Geodetic Survey (WGS) Coordinates, etc.
Map displays typically indicate position by an icon or other indicator visible on a map. One such map display, typically referred to as a moving map display, displays the position of the SATPOS in the center of the displayed map. Such map displays typically are oriented such that the top of the SATPOS device""s display indicates North (either magnetic North or true North). That is, irrespective of the direction in which the SATPOS device is actually oriented, North is shown at the top of the display. For users that intuitively know which direction is North, such maps are adequate for locating features displayed on the map. However, for users that do not know where North is, or when visibility is obscured such that the user cannot determine where North is, such maps are inadequate for guiding the user to a destination or feature on the map.
For many commercial applications of SATPOS systems, such as construction site planning and management, surveying, navigation, etc., it is essential that an operator be able to locate features displayed on the map. Such users typically operate a separate device for indicating direction such as a conventional magnetic compass.
Some SATPOS devices indicate the direction of movement of the SATPOS device, typically referred to as xe2x80x9cheading.xe2x80x9d Typically, heading is determined by analysis of determined position in relation to prior determinations of position as the SATPOS moves. Typically, SATPOS devices that indicate heading use a map display oriented such that the top of the SATPOS unit (e.g., the top of the unit""s display) corresponds to North(either magnetic North or true North).
Some prior art SATPOS devices orient the displayed map such that the top of the SATPOS unit (e.g., the top of the unit""s display) corresponds to the direction of movement calculated by the SATPOS device. This gives a good approximation of the user""s heading as long as the user continues to move and as long as the SATPOS unit is oriented in the direction of movement, allowing a user to easily determine the location of features visible on the display.
However, when the SATPOS device stops moving, determination of heading can no longer be made. Some SATPOS systems maintain the previous heading for orienting the moving map display for a given time interval. Other prior art SATPOS systems default to positioning North at the top of the map. This can be quite confusing to the user.
Recently, digital compasses have been developed that can indicate direction. However, digital compasses must be calibrated to properly align the digital compass prior to use. Also, each time that magnetic environment around the compass changes, the digital compass must be recalibrated. Digital compasses are typically calibrated by moving the digital compass in a full horizontal arc. The calibration process takes time and is prone to operator error. Also, calibration error can occur as a result local magnetic anomalies.
Some SATPOS devices calculate and display the relative positions of each of the satellites from which signals are being received. These displays are commonly referred to as skyplots. Skyplots are important for indicating the number and relative location of satellites. This allows a user to determine when an obstruction such as, for example, a mountain, tall building, tree, etc., is blocking reception of satellite signals. By visually analyzing the relative locations of the received satellites, the user can move in order to optimize the number of satellites being received and the geometry relating to the received satellites. This allows for more accurate determination of position by moving so as to avoid the obstruction.
However, skyplots conventionally are displayed such that north is at the top of the display. Therefore, unless the user is able to determine which direction is North, the user cannot determine the relative direction from which satellite reception is blocked. Thus, in order to effectively use a skyplot, the user must typically operate a separate device for indicating direction such as a conventional magnetic compass.
What is needed is a method and apparatus for providing an accurate indication of heading to a user of a SATPOS device. Also, a method and apparatus is needed that meets the above needs and that accurately indicates direction when the SATPOS is not moving. Also, a method and apparatus is needed that is easy to use and that does not require a user to manually calibrate a compass. Moreover, a method and apparatus for generating a skyplot is needed that indicates the orientation of the satellites of a skyplot such that the location of the satellites can be easily determined by a user. The present invention meets the above needs.
The present invention provides a method and apparatus that accurately indicates direction and heading to a user of a satellite positioning system (SATPOS) device. The integrated position and direction system of the present invention includes a digital compass for indicating direction when the SATPOS is not accurately determining direction.
An integrated position and direction system is disclosed that includes a SATPOS having a receiver adapted to receive satellite position determining signals. The integrated position and direction system of the present invention also includes a digital compass that is adapted to determine direction.
The integrated position and direction system also includes a controller for controlling the operations of the integrated position and direction system. The controller is coupled to the SATPOS, the digital compass, and to a display.
In one embodiment of the present invention, when the SATPOS is moving, the direction of movement or xe2x80x9cheadingxe2x80x9d determined by the SATPOS is indicated on the display. When the SATPOS is not moving, the direction given by the digital compass is indicated on the display. Therefore, while the SATPOS is moving, the heading is indicated, and when the SATPOS is not moving, direction is indicated using the digital compass. Thus, the present invention provides a method and apparatus for providing an accurate indication of both heading and direction to a user of a SATPOS device.
In one embodiment, the digital compass is automatically calibrated by the SATPOS when the SATPOS is moving. This calibration can be initiated by the user or can be fully automatic. More particularly, the digital compass of the present invention is calibrated automatically, either as a result of user input (e.g., selection of an icon, pressing of a button, etc.), or as a result of user-defined criteria for automatic calibration. That is, the user can program the present invention to automatically calibrate the digital compass (e.g. when velocity exceeds a given threshold, whenever the SATPOS begins moving, periodically while the SATPOS is moving, when the difference between the SATPOS determined heading differs from the heading indicated by the digital compass by more than a predetermined threshold, etc.) Thus, the position and direction system of the present invention is easy to use because there in no need for a user to calibrate a compass as is required using a prior art compass alone.
In one embodiment a method and apparatus for generating a skyplot is disclosed. In one embodiment of the present invention, the satellites of the skyplot are oriented according to the orientation of the integrated position and direction system. Thus, no matter what the orientation is of the position and direction system, the skyplot is properly oriented such that the user can easily determine the location of the satellites of the skyplot. In addition, when the orientation of the position and direction system is changed, the skyplot rotates such that the correct orientation of the satellites of the skyplot is always indicated relative to the orientation of the position and direction system.
In another embodiment of the present invention, the skyplot is oriented using both the heading determined by the SATPOS and using the direction determined by the digital compass. In this embodiment, when the SATPOS is moving, the direction of movement or SATPOS is not moving, the direction given by the digital compass is used to orient the displayed skyplot. Because the skyplot is always oriented relative to the integrated position and direction system, either based on the direction indicated by the digital compass or based on the movement of the integrated position and direction system, the user can easily determine the location of satellites of the skyplot. Also, the user can easily determine features that are obstructing satellite reception without any need for the user to determine the location of North as is required when using a prior art skyplot display.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments that are illustrated in the various drawing figures.